The need for thinner and stiffer bases for imaging products is well recognized. In addition to providing cost advantages, thinner supports may fulfill many other criteria. For example, in motion picture and related entertainment industries, thinner photographic base allows for longer film footage for the same sized reels. Display materials, such as photographic papers, should be light in weight and flexible for particular applications. For instance, when the photographs are mailed or used as a laminating material, it is desirable that the materials be light in weight. When stored in albums, reduced thickness of the paper will minimize undesirable bulkiness. For some uses, such as for a stand-up display and to convey a sense of value, it is desirable that the photographs have a heavy stiff feel. The cost of forming stiff paper is substantial, as increases in the amount and stiffness of the raw materials are expensive. It would be desirable if photographic materials could be easily produced with a variety of stiffness and caliper characteristics so that a variety of consumer desires could be easily met.
Unfortunately, a reduction in thickness of the base typically results in a reduction in stiffness, which may have detrimental effects in terms of, for example, curl, transport, and durability. In addition, changes, that is, increases or decreases, in caliper that are required for papers of increased or decreased stiffness lead to difficulties in handling in film manufacturing machines and in development after exposure.
Efforts to control the deleterious properties resulting from the use of thinner films or supports have included the use of one or more curl control layers on the back-side of the support of a photographic film element. The curl control layer or layers prevent excessive curl in the element upon drying of the coated light-sensitive layers. The curl control layers also prevent curl when the exposed film is developed and ensure that the film element remains sufficiently flat in a camera or printer during exposure and printing to optimize focus conditions. The clay-containing layer facilitates transport of the film through a camera and processing apparatus.
Back-side curl control layers typically comprise a hydrophilic binder coated from an aqueous formulation, and are of sufficient total thickness upon drying (generally from 1–25 micrometers) to off-set the curl generated by the hydrophilic binder layers on the light-sensitive emulsion layer side of the support. The use of curl control layers is especially important where a transparent magnetic recording layer is included in relatively wide (that is, wider than 35 mm) roll camera films, such as 120 and 220 medium format films, and sheet films including x-ray and graphic arts films, as such films are generally more sensitive to curl and the resulting degradation of magnetic recording performance associated with variable head-media spacing. Optimized ratios of the thicknesses of light sensitive layers, magnetic recording layers, and curl control layers comprising hydrophilic colloids in photographic elements for curl control are described, in U.S. Pat. No. 5,753,426, and U.S. Pat. No. 5,866,287, the disclosure of which is incorporated by reference herein.
Polymeric thin film and coatings have been widely used to improve the overall stiffness of an imaging element. Polymeric thin films are also used as the curl control layer. However, the mechanical properties of the polymeric thin films are limited by the material used to make the coatings. Different methods have been utilized to enhance the properties of these thin films, such as using higher molecular weight polymer, adding toughening agent, and adding fiber and inorganic filler. However, the introduction of the foreign materials into the system often deteriorates the optical clarity of the film.